Latch insulation for quick break circuit breakers



Feb. 1, 1955 w. H. EDMUNDS 2,701,284

LATCH INSULATION FOR QUICK BREAK CIRCUIT BREAKERS Filed May 28 1953 United States Patent LATCH INSULATION FOR QUICK BREAK CIRCUIT BREAKERS William Harold Edmunds, Havertown, Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa.

Application May 28, 1953, Serial No. 358,156

4 Claims. (Cl. 200116) My invention relates to quick break circuit breakers and is more particularly directed to a novel arrangement and method whereby an insulated latch prevents parallel current flow from the bimetallic trip unit through the cradle mechanism of the circuit breaker.

In the prior art, the metallic latch member is insulated from the bimetallic element by sandwiching a piece of fish paper between the latch and the bimetallic element. In this arrangement, it was also necessary to provide some insulation for the metallic rivet which secured the metallic latch to the bimetallic trip unit. However, the fish paper type of insulation has the disadvantage of complicating the assembly of the quick break circuit breaker and thus increasing the cost of the final article.

That is, since it is necessary for the assembler to perform the additional operation of placing the fish paper between the latch and insuring that it is properly positioned, the added time and material result in a considerable increase of the assembly costs of this relatively inexpensive breaker.

lt is noted that since the latch member must have a relatively strong surface to hold and maintain the cradle in latched position, it is necessary that the surface there of be hard and hence, must be a metallic member.

In my novel arrangement and method, I provide a light coat of chromic oxide film on the latch member which serves to insulate this unit from the bimetal to which it is attached. The rivet which is used to secure the latch member to the bimetallic element can be also provided with a layer of chromic oxide to insure complete insulation between the bimetallic member and the latch member and thereby prevent a parallel path of current flow through the cradle mechanism.

Accordingly, a primary object of my invention is to provide a novel arrangement for quick break circuit breakers in which the insulation between the cradle mechanism and the bimetallic element results from the characteristics of the latch member.

Another object of my invention is to provide a quick break circuit breaker in which the parallel path comprising the bimetal, latch member and cradle will not conduct current due to an oxide coating on the latch member.

Still another object of my invention is to provide a latch member which insulates the bimetal from the cradle without the necessity of providing additional insulation means.

These and other objects of my invention will be apparent from the following description when taken in connection with the drawings in which:

Figure l is a side view of the operating mechanism of a quick break circuit breaker to which my invention is particularly adaptable. This figure illustrates the position of the components when the circuit breaker is in the fully closed position with latch engagement between the cradle and the latch member.

Figure 2 is an exploded perspective view illustrating the relationship and connection of the bimetallic element, the latch member, and the armature by means of metallic rivet. This figure illustrates a modification of my invention which can be used when a non-oxidized or non-plastic rivet is used.

The circuit breaker is provided with a molded housing 11 having its various components side mounted in appropriate grooves and recesses thereof. The stationary contact 12 is electrically connected to the female terminal 13 by the terminal conductor 14. The movable contact 15 is secured to the contact arm 16. An arc chute Patented Feb. 1, 1955 17 is provided to extinguish between the are created by the separation of the movable contact 15 from the stationary contact 12.

The spring 19 connected at one end to the movable contact arm 16 and at its other end to the U-shaped cradle member 20 maintains contact pressure. That is, the movable contact 16 is pivoted in grooves in the bottom portion of the circuit breaker handle 22 and hence, the spring 19 will bias the contact arm toward the left.

A pigtail 23 is brazed at one end 24 to the movable contact arm 16 and at the other end 26 to the lower portion of the bimetallic element 27. The bimetallic element 27 at its upper end is brazed to the terminal member 29. Screw 28 is in threaded engagement with bimetal 27 and terminal 29 to provide calibration adjustment. The terminal member 29 is seated in the recess 30 of the molded housing 11 and has a terminal connecting portion 32. Thus, the normal flow of current through the quick break circuit breaker is as follows: From terminal connector 32 through terminal 29, screw 28, bimetallic element 27, through its end 26 to the pigtail 23 and from connection 24 to the movable contact arm through the movable contact 15 to the stationary contact 12 through conductor 14 to the other terminal 13 of the circuit breaker.

An L-shaped latch member 40 is secured to the bimetallic element 27 by means of the rivet 41. The rivet 41 also secures the armature 42 to the bimetal 27. A cradle 20 is rotatably mounted on the permanent pivot 43. Thus, as shown in Figure 1, the cradle 20 although biased in a clockwise direction around the pivot 43 is prevented from rotating due to the engagement of the cradle surface 45 with the latch surface 46 of the L-shaped latch member 40.

On the occurrence of an overcurrent, the bottom portion of the bimetal 27 will deflect to the right thereby releasing the latch engagement 45, 46 of the cradle 20. In the event a severe short circuit occurs, the armature 42 will be attracted toward the magnet 50 thereby moving the bottom portion of the bimetal 27 to the right to thereby release the latch engagement 45, 46. When the latch 45, 46 is disengaged either by the time delay trip of the deflection of bimetal 27 or due to instantaneous trip due to the attraction of the armature 42 to the magnet 50, spring 19 will rotate the cradle 20 around its pivot 43 thereby placing the spring 19 on the right side of the contact arm 16 and effecting disengagement of the cooperating contacts 12 and 15.

However, when the contacts are in engagement and the cradle 20 is latched to the member 40 at 45, 46, an alternate parallel path for the load current exists as follows: from the bimetal 27 to the latch member 40 either directly or through the metal rivet 41 to the cradle 20 thence to the contact arm 16 either directly or through the spring 19 to the movable contact 15. However, since these components are not designed to carry the load current, it is highly undesirable to have this parallel path exist for current flow.

Hence, my invention is directed to a novel arrangement whereby the bimetallic element 27 will be insulated from the cradle 20.

The prior art method mentioned in the introduction of this specification provided the sandwiching of a piece of fish paper between the L-shaped latch member 40 and the bimetal 27 with an insulating sleeve over the rivet 41 to thereby prevent any current flow from the bimetal 27 to the latch member 40. However, this method, as noted in the introduction, is highly undesirable and my invention is particularly directed to a novel insulating arrangement which overcomes the prior art disadvantages.

In my novel arrangement, the latch member 40 is provided with a light coat of chromic oxide. This is done as follows:

The latch member 40 is a stainless steel member with high chrome content. such as a stainless steel member 40. It is possible to heat treat this material and form a chromic oxide which is a good insulator. The chromic oxide coat is achieved by placing the high chrome content stainless steel latch member 40 in a standard type furnace, such as the Lindberg furnace, using a ratio of 4.5 air to 1.0 gas for the atmosphere. The stainless steel member which is to be used for the latch member 40 is heat treated to between 850 and 875 degrees Fahrenheit for thirty minutes and then allowed to cool in a chamber under the atmosphere present. This operation forms a light coat of chromic oxide and also hardens the stainless steel thereby providing a very good latching surface.

It will be noted that the latch member 40 can also be obtained with the characteristics just described in connection with stainless steel members by starting with a piece of metal which has high hardness and then coating same either by oxidizing or other means with an insulation film.

It will be noted that even though the latch surface 46 of the latch member 40 is polished to provide a smooth surface for engagement with portion 45 of the latch that the insulation characteristics of the latch member will be retained. That is, since the latch surface 46 does not come into contact with the bimetallic element 27, the chromic oxide coating thereon can be removed without affecting the insulating characteristics between the bimetal 27 and the cradle 20.

Although the surface 51 of the latch member 4% which engages the bimetal 27 is a chromic oxide coating to thereby prevent direct current flow from the bimetal to the latch member, it will also be necessary to provide means to prevent current flow from the bimetal 27 through the rivet 41 of the latch member 40. This can be achieved in any one of a number of ways.

The first method is to provide a rivet 41. which has an oxide coating placed thereon similar to the manner above described in connection with the latch member 40. Hence, the insulation characteristics will be the result of the coating and no current will be permitted to flow either directly from the bimetal to the latch mem ber 40 or through the alternate path from the bimetal to the rivet of the latch member.

The second arrangement for preventing current flow through the rivet is to provide a plastic rivet 41. Plastic rivets of the type having insulating characteristics to prevent current fiow from the bimetal to the latch member are commercially available and easy to assemble.

The third method of preventing current flow from the bimetal to the latch member is illustrated in Figure 2. In this arrangement, the opening in the latch member 40 which receives the rivet 41 has a much larger diameter than the diameter of the shaft of the rivet. Thus, the rivet 41 will maintain the latch 40 sandwiched between the armature 42 and the bimetal 27 even though the shaft of the rivet 41 does not touch the latch member 40 due to its large opening 53.

Thus, by providing an oversized hole 53 in the latch member 40, it is still possible to use a standard metallic type rivet 41 since the surface 51 of the latch member 40 has an insulating coat to prevent direct current flow from the bimetal to the latch member.

Thus, it will be noted that with the particular design set forth above, the insulating coat 51 is provided on the latch 40 and not on the cradle 20. However, the latching compounds on both the cradle 20 and the latch member 40 can be polished thereby eliminating any oxide coating which may be present.

As noted, it is possible to clean off the oxide on the latching surface 46 of the latch member 40 and still retain an insulated oxide coating 51 to form an insulator at the surface where the latch member 40 engages the bimetal 27.

In the foregoing, I have described my invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordingly, I prefer to be bound not by the specific disclosure herein but only by the appending claims.

I claim:

1. A quick break circuit breaker having a molded housing and a pair of cooperating contacts having an engaged and disengaged position; latch means to maintain said cooperating contacts in engagement; said latch means comprising a cradle and a latch member; said latch member riveted to a bimetallic element of said quick break circuit breaker; said rivet and said latch member having an oxide coating to prevent current flow from said bimetal to said cradle.

2. A quick break circuit breaker having a molded housing and a pair of cooperating contacts having an engaged and disengaged position; latch means to maintain said cooperating contacts in engagement; said latch means comprising a cradle and a latch member; said latch member riveted to a bimetallic element of said quick break circuit breaker; said latch member having a chromic oxide coating; said rivet being a plastic material; said plastic rivet and said chromic oxide coating on said latch 1116111111361 preventing current flow from said bimetal to said cra e.

3. A quick break circuit breaker having a molded housing and a pair of cooperating contacts having an engaged and disengaged position; latch means to maintain said cooperating contacts in engagement; said latch means comprising a cradle and a latch member; said latch member having an opening to receive a rivet; said rivet securing said latch member to a bimetallic element of said quick break circuit breaker; the diameter of the opening of said latch member being larger than the diameter of the head of said rivet; said latch member being made of a high chrome content stainless steel having a chromic oxide coating; said rivet securing said latch member to said bimetal Without engagement therewith; said opening and said chromic film of said latch member preventing current flow from said bimetal to said latch member.

4. A quick-break circuit breaker having a molded housing and a pair of cooperating contacts having an engaged and disengaged position; a latch means to maintain said cooperating contacts in said engaged position; said latch means comprising a cradle and a metal latch member; said metal latch being made of a high chrome content stainless steel having a chromic oxide coating thereon; said metal latch member secured to a bimetallic element of said circuit breaker by means of a rivet; said rivet being made of a high chrome content stainless steel having a chromic oxide coating; said rivet and said metal latch member providing a high resistance path between said bimetal and said cradle.

References Cited in the file of this patent UNITED STATES PATENTS 2,199,622 Dorfman May 7, 1940 2,406,325 Dorfman Aug. 27, 1946 2,454,106 Von Hoorn Nov. 16, 1948 2,455,753 Getchell Dec. 7, 1948 

